The speed of modern ink jet printers has to increase steadily for economic reasons. Particularly suitable recording sheets for such printers comprise nanoporous inorganic compounds such as for example silicium dioxide, aluminum oxide/hydroxide, aluminum oxide or their mixtures. Such recording sheets are known as “nanoporous recording sheets”. Images printed onto these recording sheets need to have a good storage stability even under adverse conditions. This can only be achieved by using a finely tuned system of inks, respectively the dyes contained therein.
Up to now, these images do not satisfy all required properties. In particular, the water fastness, the light stability, the ozone stability, the hue and the brilliance of images printed onto these recording sheets are not satisfactory. Thus, new dyes are looked for which would improve the properties mentioned above of images printed onto these recording sheets, in particular in areas with black hue.
Although quite a number black dyes have already been proposed as black dyes for ink jet printing. However, none satisfies all of the required properties.
The trisazo dye of formula (I)
is described in patent application WO 2005/054,374 (example 1-5).
The trisazo dye of formula (II)
is described in patent application WO 2005/054,374 (comparative example 1-2).
The trisazo dye of formula (III)
is described in patent application JP 2005/220′211 (compound no. 17).
These trisazo dyes, representing the state of the art, do not satisfy all the required demands if they are used in the formulation of recording liquids for ink jet printing that should provide images having a good stability even under adverse conditions on rapidly drying nanoporous recording sheets. Evidently, they also need to give black image regions or colorings having an as far as possible neutral black hue (values of L*a*b* with the lowest possible values of a* and b*) on any other type of recording sheet such as plain or coated paper, coated or uncoated, opaque or transparent synthetic materials.
Dyes used for the preparation of such inks need to have a good solubility in the essentially aqueous ink liquid, they have to penetrate into the recording sheet and should not show dye aggregation on the surface of the recording sheet (“bronzing”). They need to provide printed images having high optical density, good water fastness, good light stability, good ozone fastness and good diffusion fastness even under adverse conditions. They need to be stable in the ink even when the ink is stored for a long time under adverse conditions.
Various types of ink compositions have been proposed. Typical inks comprise one or more dyes or pigments, water, organic co-solvents and other additives.
The inks have to satisfy the following criteria:                (1) The ink gives images of excellent quality on any type of recording sheet.        (2) The ink gives printed images exhibiting good water fastness.        (3) The ink gives printed images exhibiting good light stability.        (4) The ink gives printed images exhibiting good ozone fastness.        (5) The ink gives printed images exhibiting excellent smudge behavior.        (6) The ink gives printed images exhibiting excellent storage stability under conditions of high temperature and humidity.        (7) The ink does not clog jetting nozzles of the ink jet printers even when these are kept uncapped while recording is suspended for long periods.        (8) The ink may be stored for long periods without deterioration of its quality.        (9) The ink has to be non-toxic, non-flammable and safe.        